This invention, in its broadest aspect, pertains to the utilization of naturally occurring variations in ambient outdoor temperature to reduce water vapor in the air inside a storage container the contents of which may suffer damage or deterioration should such water vapor condense thereupon.
The dehumidifier construction disclosed herein is operable to vent air from inside a storage container when such air is heated and expanded in response to the natural daytime rise in ambient temperature and to admit outside air into the container when the air inside is cooled and contracted in response to the natural nighttime drop in ambient temperature. If there is no temperature differential between air inside and outside the container, a balanced pressure condition exists and no air will be forced either into or out of the container through its vents. Cyclic or reversible air flow as described above is commonly characterized as a breathing action or respiratory function of the container.
Housings of this type which exhibit breathing action are disclosed in a Solar Activated Dehumidifier described in U.S. Pat. No. 2,462,952 issued to Dunkak and in a Solar Powered Dehumidifier Apparatus described in U.S. Pat. No. 4,242,112 issued to Jebens. These prior art dehumidifiers are of a passive class which utilize a dessicant, such as dried silica gel, to absorb water from ambient air before it is inhaled into a closed housing. Such preconditioning of ambient air by means of a dessicant prior to inhalation into a housing is preferred over the well-known refrigerating class of dehumidifiers which consume large quantities of power in order to maintain the temperature and vapor density of air inside the housing at critical levels which forstall unwanted condensation on the housing walls and on objects disposed inside the housing. Nonetheless, both Dunkak and Jebens cite the relatively high energy consumption and cost involved in periodic reactivation of dessicant material by conventional electric heating elements and fueled burners. To overcome this energy related shortcoming of dessicant type air dryers, the aforenoted inventors propose that solar radiation be used as the sole or primary heat source for releasing accumulated moisture from their respective dessicant bodies. Both of these prior art devices also utilize that air periodically exhaled from the heat-pressurized housing interior as a source of purging air to convey moisture from the dessicant body to ambient.
While passive dehumidifiers employing solar activated dessicants to precondition breathing air for a housing appear to display some operating cost advantage over air refrigerating dehumidifiers, several shortcomings remain.
The need for prolonged solar exposure restricts the choice of location of the dessicant body to a normally sunny site; and, since the dessicant body and the housing it serves are usually physically attached or in close proximity, the choice of a less sunny location for the housing, itself, may be unavailable.
To reactivate a body of dessicant material by solar heating, the dessicant material must be subjected to temperatures in excess of 300.degree. F. for a drying period related to the mass of the dessicant body. To assure that solar heating is sufficient to cause the dessicant to give up its accumulated moisture, both Dunkak and Jebens suggest that special lenses or mirrors be positioned between the dessicant body and the sun to concentrate solar rays to effect superheating of the dessicant. Solar tracking apparatus for maintaining the most advantageous position of the lenses has also been proposed. Obviously, association of such auxilliary devices with the dehumidifier apparatus would result in higher initial cost and ongoing structural vulnerability to adverse outside conditions such as wind, rain, hail and airborne particulates.
Where a dehumidifier depends exclusively upon periodic exposure to direct sunlight for proper maintainence of one of its most critical operating elements, i.e. its dessicant body, such a device may be only marginally efficient on a partly cloudy day; moreover, after a succession of cloudy days, the dessicant will likely become fully saturated and the dehumidifier will fail altogether. Provision of an oversized dessicant body will provide a margin of safety against dessicant failure but with accompanying increases in dessicant cost, bulkiness and reactivation time. Moreover, where uncertainty regarding the frequency and duration of sunlight renders the risk of dessicant failure absolutely unacceptable, a standby, conventionally powered dehumidifier must be kept ready in case of such failure thereby defeating in large part the major purpose of a passive dehumidifier.
If the volume of a housing to be dehumidified were sizable, as would be the case for a box-like container dimensioned for storing an automobile, a substantial mass of dessicant material would be required to dry efficiently such a large volume of air to be inhaled into the housing. Provision of ample dessicant would be expensive; and, the bulk of the required dessicant body would be cumbersome to install initially and to replace from time to time as required. Likewise, a storage space suitably sized to accommodate the dessicant body would significantly increase the overall size and cost of the dehumidifier apparatus.
The foregoing recitation of the problems which remain in the construction and application of conventional passive dehumidifier devices of the respiratory type suggests that a substantial change in concept and design is needed to provide an improved passive dehumidifier which exhibits these surprisingly different characteristics and capabilities:
1. No air drying agent such as dessicant material is required. PA1 2. Preconditioning of inhaled air is independent of the availability of sunlight as a reliable source of radiant energy. PA1 3. Daily respiration of the housing can be managed so that inhalation and exhalation occur only as and when outside air conditions favor efficient dehumidification of the housing. PA1 No dessicant or other air-drying agent need be employed or reconditioned. PA1 No energy source other that naturally occurring atmospheric warming is required. PA1 The storage means may be sited anywhere out of doors without regard to conditions of sunlight or shade. PA1 The storage means may be located interiorly of a larger structure provided it remains subject to daily fluxuations in outdoor temperature. PA1 The storage means and items placed therein require no inspection or maintenance over long periods of time. PA1 The hereindisclosed means for dehumidification permits the use of large housing structures capable of storing large, bulky items such as automobiles, for example.